Ch 8 Muscles Introduction: A. All movements require muscle which are organs using chemical energy to contract. B. The three types of muscle in the body are skeletal, smooth, and cardiac muscle. C. This chapter focuses on skeletal muscle. Structure of a Skeletal Muscle A. Each muscle is an organ, comprised of skeletal muscle tissue, connective tissues, nervous tissue, and blood.
1. B. Connective Tissue Coverings a. 1. Layers of dense connective tissue, called fascia, surround and separate each muscle. 2. This connective tissue extends beyond the ends of the muscle and gives rise to tendons that are fused to the periosteum of bones. 3. Sometimes muscles are connected to each other by broad sheets of connective tissue called aponeuroses. 4. The layer of connective tissue around each whole muscle is the epimysium: the perimysium surrounds individual bundles (fascicles) within each muscle; and each muscle cell (fiber) is covered by a connective tissue layer called endomysium. Study Analogy Pretend you are going to play a joke on someone and give them 100 pencils. The pencils will represent muscle fibers. First you wrap each individual pencil in tissue paper (dense tissue paper of course!). This would be endomysium. Then you take about 10 pencils in a bundle (a fascicle) and wrap them in paper (perimysium). After that you take all the bundles and wrap them in gift wrap (epimysium). But you are going to mail this joke, so you also have to wrap it in brown paper representing the fascia. C. Skeletal Muscle Fibers 1. Each muscle fiber is a single, long, cylindrical muscle cell. 2. Beneath the sarcolemma (cell membrane) lies sarcoplasm (cytoplasm) with many mitochondria and nuclei; the sarcoplasm contains myofibrils.
a. Thick filaments of myofibrils are made up of the protein myosin. b. Thin filaments of myofibrils are made up of the protein actin. c. The organization of these filaments produces striations. 3. A sarcomere extends from Z line to Z line. a. I bands (light bands) made up of actin filaments are anchored to Z lines. filaments. only. b. A bands (dark bands) are made up of overlapping thick and thin c. In the center of A bands is an H zone, consisting of myosin filaments 4. Beneath the sarcolemma of a muscle fiber lies the sarcoplasmic reticulum (endoplasmic reticulum), which is associated with transverse (T) tubules (invaginations of the sarcolemma). and is open to the a. Each T tubule lies between two cisternae of the sarcoplasmic reticulum outside of the muscle fiber. b. The sarcoplasmic reticulum and transverse tubules activate the muscle contraction mechanism when the fiber is stimulated.
D. Neuromuscular Junction junction. 1. The site where the motor neuron and muscle fiber meet is the neuromuscular a. The muscle fiber membrane forms a motor end plate in which the sarcolemma is tightly folded and where nuclei and mitochondria are abundant. b. The cytoplasm of the motor neuron contains numerous mitochondria and synaptic vesicles storing neurotransmitters. E. Motor Units 1. A motor neuron and the muscle fibers it controls make up a motor unit; when stimulated to do so, the muscle fibers of the motor unit contract all at once.
Skeletal Muscle Actions A. Origin and Insertion 1. The immovable end of a muscle is the origin, while the movable end is the insertion; contraction pulls the insertion toward the origin.
2. Some muscles have more than one insertion or origin. B. Interaction of Skeletal Muscles prime mover. antagonists. 1. Of a group of muscles, the one doing the majority of the work is the 2. Helper muscles are called synergists; opposing muscles are called Major Skeletal Muscles A. Muscles are named according to any of the following criteria: size, shape, location, action, number of attachments, or direction of its fibers. B. Muscles of Facial Expression 1. Muscles of facial expression attach to underlying bones and overlying connective tissue of skin, and are responsible for the variety of facial expressions possible in the human face. 2. Major muscles include epicranius, orbicularis oculi, orbicularis oris, buccinator's, zygomaticus,
C. Muscles of Mastication 1. Chewing movements include up and down as well as side-to-side grinding motions of muscles attached to the skull and lower jaw. 2. Chewing muscles include masseter and temporalis. D. Muscles that Move the Head 1. Paired muscles in the neck and back flex, extend, and turn the head. 2. Major muscles include sternocleidomastoid, splenius capitis, and semispinalis capitis. E. Muscles that Move the Pectoral Girdle 1. The chest and shoulder muscles move the scapula. 2. Major muscles include trapezius, rhomboideus major, levator scapulae, serratus anterior, and pectoralis minor.
F. Muscles that Move the Arm 1. Muscles connect the arm to the pectoral girdle, ribs, and vertebral column, making the arm freely movable. 2. Flexors include the coracobrachialis and pectoralis major. 3. Extensors include the teres major and latissimus dorsi. 4. Abductors include the supraspinatus and the deltoid. 5. Rotators are the subscapularis, infraspinatus, and teres minor. G. Muscles that Move the Forearm the ulna and radius. 1. These muscles arise from the humerus or pectoral girdle and connect to 2. Flexors are the biceps brachii, brachialis,and brachioradialis.
3. An extensor is the triceps brachii muscle. 4. Rotators include the supinator, pronator teres, and pronator quadratus. H. Muscles that Move the Wrist, Hand, and Fingers 1. Movements of the hand are caused by muscles originating from the distal humerus, and the radius and ulna. 2. Flexors include the flexor carpi radialis, flexor carpi ulnaris,
palmaris longus, and flexor digitorum profundus. 3. Extensors include the extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, and extensor digitorum. I. Muscles of the Abdominal Wall girdle. 1. This group of muscles connects the rib cage and vertebral column to the pelvic a. A band of tough connective tissue, the linea alba, extending from the xiphoid process to the symphysis pubis, serves as an attachment for certain abdominal wall muscles. 2. These four muscles include: external oblique, internal oblique, transverse abdominis, and rectus abdominis. J. Muscles of the Pelvic Outlet 1. The superficial urogenital diaphragm fills the space within the pubic arch, and the deeper pelvic diaphragm forms the floor of the pelvic cavity. 2. Pelvic diaphragm ncludes the levator ani.
3. Urogenital diaphragm: includes the superficial transversus, perinei, bulbospongiosus, and ischiocavernosus. K. Muscles that Move the Thigh girdle. 1. The muscles that move the thigh are attached to the femur and to the pelvic 2. Anterior group includes the psoas major and iliacus. 3. Posterior group is made up of the gluteus maximus, gluteus medius, gluteus minimus, and tensor fasciae latae. 4. Thigh adductors include the adductor longus, adductor magnus, and gracilis. L. Muscles that Move the Leg 1. This group connects the tibia or fibula to the femur or pelvic girdle. 2. Flexors are the biceps femoris,
semitendinosus semimembranosus, and sartorius. 3. An extensor is the quadruceps femoris group made up of four parts: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius.
M.Muscles that Move the Ankle, Foot, and Toes 1. Muscles that move the foot are attached to the femur, fibula, or tibia, and move the foot upward downward, or in a turning motion. 2. Dorsal flexors include the tibialis anterior, peroneus tertius, and extensor digitorum longus.
3. Plantar flexors are the gastrocnemius, soleus, and flexor digitorum longus. 4. An invertor is the tibialis posterior. 5. An evertor is the peroneus longus.